To the bottom with thiamin deficiency
Image: Siv Huseby
Image: Siv Huseby
FEATURE Changes in the phytoplankton community can affect fish and birds, and may explain why vitamin deficiency occurs among top predators.
Several top predators in the aquatic food chain have shown signs of vitamin deficiency, more specifically, lack of thiamin, B1 . Salmon have had problems with reproduction, and mortality among the common eider is very high. The question is why this thiamin deficiency arises. To get to the bottom of the problem, a research group within EcoChange has examined the part of the food web where everything begins: phytoplankton and zooplankton.
Thiamin is an essential vitamin for virtually all living organisms. It is needed for basic metabolism, and thiamin deficiency leads to a variety of symptoms. Behavioral changes, weakened immune system and serious reproductive effects are among them.
In the aquatic environment, thiamin is primarily produced by phytoplankton and bacteria. This means that all animals must receive the compound via ingestion. The body cannot store any large quantities either, but must receive a continuous supply of it via food. Also, not all species of phytoplankton can produce thiamin. The species composition of phytoplankton is therefore important for the availability of thiamin.
Phytoplankton composition may explain why animals higher up in the marine food web are affected by thiamin deficiency.
ImageIve van KrunkelsvenFilamentous cyanobacteria bloom annually in the Baltic Sea, and have been found to contain relatively large amounts of thiamin. Nevertheless, the presence of cyanobacteria appears to inhibit the uptake of thiamin by the zooplankton. Cyanobacteria provide relatively poor food for zooplankton, as they do not contain the correct fatty acids, in some cases produce toxins and the filaments are difficult for zooplankton to ingest. They also have an inhibitory effect on zooplankton reproduction, which can also affect the amount of thiamin reaching higher levels in the food web. Thus even though cyanobacteria contain high concentrations of thiamin, it is not certain that this thiamin can be transported further up into the food web.
The species composition of phytoplankton is a factor that is of great importance for how much thiamin zooplankton can get. Zooplankton grazing on phytoplankton can to a certain extent select which phytoplankton it eats, and can thus influence the species composition of the phytoplankton community.
The conclusion of the study is that the amount of thiamin in higher trophic levels, such as top predators, could be closely related to the composition of the phytoplankton community, and is adversely affected by the increasing amount of cyanobacteria in the ecosystem.
The article has earlier been published in the EcoChange annual report 2018. The text is based on: